1. Field of the Invention
This invention relates to a method for forming a pattern from a film which is deposited with low directivity.
2. Prior Art
Conventionally, refractory metal is employed in semiconductor devices. For example, W (tungsten) and W-Si (tungsten-silicide) are used for gate electrodes of FETs. W-N (tungsten-nitride) and Ta-N (tantalum-nitride) are used for thin film resistors.
Since the boiling point of the refractory metal is generally more than 5000.degree. C., it is difficult to deposit the metal by resistive heating evaporation or electron beam evaporation. Therefore, sputtering or Chemical Vapor Deposition (CVD) is employed as a deposition process with low directivity.
A prior method for forming a pattern of refractory metal is illustrated in FIG. 4.
First, a W-Si film 13 is formed on a Si substrate 11 by sputtering (FIG. 4A). Next, a resist pattern 15 is formed on the W-Si film 13 using photolithography technology. Then, by Reactive Ion Etching (RIE) with SF6 gas, the W-Si film 13 is etched using the resist pattern 15 as an etching mask (FIG. 4B). Next, the resist pattern 15 is removed (FIG. 4).
However, according to the above prior art, unless the etching of the W-Si film 13 is stopped in a timely manner, the Si substrate 11 is etched.
Another prior art which overcomes the above problem is illustrated in FIG. 5.
First, a resist pattern 23 is formed on the Si substrate 21 using photolithography (FIG. 5A). To facilitate the subsequent lift-off process, the resist pattern 23 includes a portion which overhangs at a window 23a.
Next, a W-Si film 25 is formed on the resist pattern 23 and the Si substrate 21 by sputtering (FIG. 5B). Due to the overhangs, of the resist pattern W-Si 23 is not deposited on the upper areas of the side walls of the resist pattern 23.
Next, the above structure is soaked in a resist dissolver. The dissolving of the resist pattern 23 starts from the exposed areas where the W-Si is not deposited. As such, lift-off is performed to form the W-Si pattern 25a (FIG. 5C).
However, according to this prior art, method the exposed resist area tends to be small. Thus, a relatively large amount of time, is required to dissolve the resist pattern 23.